A metal-insulator-insulator-metal (MIIM) diode includes two electrical insulators between two types of metals. The insulators and metals may be tailored such that a quantum well forms between the two insulators in response to application of a forward bias, enabling high-energy quantum tunneling. When a voltage is applied to the top metal that exceeds its threshold, tunneling electrons are accelerated across the quantum well. Quantum tunneling may be faster than charging a switch junction in an integrated circuit, partially because charge may travel faster through metal than it would through other materials (such as, for example, silicon).
MIIM diodes have a sharper forward current-to-voltage (I-V) curve than metal insulator metal (MIM) diodes. The MIIM diodes may be used as tunneling devices with very high speed performance capability, and may be compatible with many substrate technologies. MIIM diodes may be used as select devices. The utilization of MIIM diodes may reduce cost and size, and improve performance of high-speed memory devices relative to utilization of other types of select devices.
However, the insulator materials used in MIIM diodes are relatively thin compared to the de Broglie electron wavelength and, thus, conventional deposition processes may cause undesirable chemical intermixing at the interfaces of the metals and insulators. Moreover, for the MIIM to function as a diode, there will be a preferred tunneling direction that results in a sharp bend in the diode forward characteristic current-voltage (I-V) curve. As a result of the high electric fields at the contact periphery or interface current caused by electron traps at the metal-insulator interface, significant edge leakage may occur in MIIM diodes. Due to high leakage currents, MIIM diodes may generally exhibit poor rectifying behavior. Increased asymmetry and nonlinearity in the I-V performance as might be achieved through avoidance of the aforementioned chemical intermixing and edge leakage exhibited by conventional MIIM diodes may result in improved performance of MIIM diodes.
In view of the above, it would be desired to develop MIIM diodes that may be scaled to smaller sizes while exhibiting an increased asymmetrical I-V curve and associated improved rectifying behavior, as well to develop methods of forming such MIIM diodes.